Noting that the optical part of a hybrid wireless- optical broadband access network (WOBAN) has high capacity, we need to enhance the capacity for wireless access using a low-cost solution. Our prior work developed a solution where each wireless node was equipped with a single radio. Deploying multiple radios, say two, at each node will improve the performance of wireless access, but this will also increase the cost of the solution. However, deploying multiple radios at only a few nodes, especially those that are overloaded with traffic, can lead to a less-costly solution, possibly without sacrificing performance. Hence, we study how to optimally place a limited number of additional radios at the wireless nodes to save the overall network cost. We formulate this problem as an Integer Linear Program (ILP) and solve it using a standard solver such as CPLEX. As expected, by deploying multiple radios at bottleneck wireless nodes, we can obtain almost the same performance as a WOBAN with multi-radios at all nodes.

We investigate dynamic bandwidth allocation with flexible transmission rates for deadline-driven requests (DDRs) in wavelength-division multiplexing (WDM) mesh networks. DDRs provide more scheduling flexibility to the network operator compared with typical requests with no deadline and requiring a fixed bandwidth. By choosing the bandwidth and adapting the transmission rate depending on network state, the network's performance can be improved. We investigate several bandwidth allocation policies and study their benefits on network performance. Our investigation shows that an adaptive policy generally performs the best. Further improvement can be achieved by using dynamic readjustment of the allocated bandwidth.

Hybrid wireless-optical broadband access network (WOBAN) is a combination of wireless and optical networks to optimize the cost and performance of an access network. Wireless nodes collect traffic from end users and carry them to the optical part of a WOBAN using multiple hops, accumulating delay at each wireless node. Moreover, the radio capacity on each wireless link limits the capacity on each outgoing link from the node in a single-radio wireless mesh network (WMN) of a WOBAN. Thus, delay and capacity limitation in the WMN of a WOBAN is a major bottleneck. We design a capacity and delay aware routing scheme, CaDAR, to minimize the delay and increase network support in the WMN of a WOBAN. Our analysis shows that CaDAR is an efficient routing scheme for a single-radio WMN for a WOBAN that can support much higher load and has lower system delay than other approaches because of better load balanced routing.

In the challenging social/geographical environment in Africa, how to design a robust network while tolerating the traffic imbalance is studied in this paper. We propose the Africa TWO network which connects all countries in Africa by employing two concentric rings. We investigate an Integer Linear Programming model and develop heuristic algorithms to deal with some special issues in Africa, such as a large desert in North Africa, high-speed network connectivity to the rest of the world through a few existing undersea fiber cables, and traffic imbalance caused by the differential populations of the various countries. To further exploit the properties of the designed network, we propose Little-Arc-First (LAF) routing algorithm, First-Matching (FM) wavelength assignment, and Sharing Peer Protection (SPP) scheme. The proposed algorithms LAF and FM are more efficient than existing algorithms. Sharing Peer Protection (SPP) scheme achieves high reliability in a cost- effective manner. We also address how to upgrade the network to achieve longer network lifetime for overall economic benefit. Our simulation experiments demonstrate that the concentric two-ring network is a natural candidate not only for the African continent, but can also be extended to other countries and regions.

In a WOBAN, the back end is a wired optical network, the front end is managed by wireless connectivity, and, in between, the tail ends of the optical part [known as optical network unit (ONU)] communicate directly with wireless access points (AP). We study a WOBAN deployment scenario and investigate an algorithm to optimize the placement of multiple ONUs. To obtain some representative data on locations of typical wireless users, we have conducted a survey on the distribution and types of wireless routers in the Wildhorse residential neighborhood of North Davis, CA. We also formulate the multiple-ONU deployment problem using a combinatorial optimizer, viz., simulated annealing. Having found the suitable locations for ONUs, we compare the expenditures of a WOBAN vs. a wired access solution, namely Passive Optical Network (PON). To capture the challenges behind a complete WOBAN setup, we propose and investigate a joint optimization algorithm, which considers design aspects of both the wireless front end, such as avoiding interference among neighboring APs, and the optical back end, such as minimizing expensive fiber layout.

We propose a scheduling-aware burst assembly algorithm to provide bandwidth-guaranteed and delay-bounded services for IP packets in IP-over-WDM networks. To transport IP packets efficiently over a network, they are assembled into bursts, and delivered within a given deadline. All IP packets in a burst should satisfy the deadline requirement, and, in turn, all assembled bursts are guaranteed to be served. To achieve this goal, the assembly and the scheduling processes of each burst need to be performed concurrently within the same active time-window (called joint window). The joint window size is set considering the deadlines of packets in a burst so that each of them (and, in turn, the burst itself) can satisfy its deadline. To guarantee service-availability for each assembled burst, the scheduling information (e.g., when and how long a slot is free for a burst) is fed back to the burst assembly process in each joint window. This scheduling information is used to determine when and how long an assembly process will be conducted. Those packets, which can not make the deadline, are not considered for the burst assembly process. Although, in our algorithm, the packets are transmitted in a burst (as described above), we investigate the packet-level performance for a IP-over-WDM network. The simulation experiments demonstrate that our algorithm can achieve low packet loss probabilities, and guarantee the delay-bound for delivered packets (loss probability and delay-bound are key factors for emerging IP services).

Hybrid wireless-optical broadband access network (WOBAN) is a promising architecture for future network operations. Recently, the wireless part of WOBAN has been gaining increasing attention and early versions are being deployed as a municipal access solution to eliminate the wired backhaul to every wireless router. This architecture saves on network deployment costs because fiber (or wiring) does not need to extend to the end user, and it extends the reach of emerging optical access solutions, e.g., passive optical network (PON)-based access solutions. However, a major research opportunity exists in developing an efficient routing algorithm for the wireless front end of WOBAN. We propose and investigate the characteristics of "delay- aware routing algorithm (DARA)" that minimizes the average packet delay in the wireless front end of a WOBAN. We model wireless routers as queues and predict wireless link states periodically. Our simulation experiments show that DARA achieves better load balancing and less congestion compared to tradional approaches such as minimum-hop routing algorithm (MHRA) and shortest- path routing algorithm (SPRA). In addition to minimizing the delay, DARA also improves the average hop count compared to the predictive throughput routing algorithm (PTRA), a popular protocol used in several deployments for the wireless front end of a WOBAN.

The concept of a hybrid wireless-optical broadband access network (referred to as WOBAN here) is a very attractive one. This is because it may be costly in several situations to run fiber to every home from the telecom central office (CO); also, providing wireless access from the CO to every end user may not be possible because of limited spectrum. Thus, running fiber as far as possible from the CO towards the end user and then having wireless access technologies take over may be an excellent compromise. How far should fiber penetrate before wireless takes over is an interesting engineering design and optimization problem, which our study is focussing on. We propose and investigate the characteristics of a "mixed integer programming (MIP)" model for optimum placements of base stations (BS) and optical network units (ONU) in a WOBAN (primal problem). We develop several constraints to be satisfied: BS and ONU installation, user and channel assignment, and signal-quality and interference constraints. To solve this MIP with reasonable accuracy, we use "Lagrangean relaxation" to obtain the corresponding "Lagrangean dual" problem. Via simulation experiments, we verify how sensitive is the placement problem with respect to a set of chosen metrics.

In the challenging social/geographical environment in Africa, how to design a robust network while tolerating the traffic imbalance is the major goal in the paper. To achieve the goal, we propose and analyze the design of a symmetrical concentric two-ring network to connect all countries in Africa. We develop optimization schemes while dealing with some special issues in Africa, such as a large desert in North Africa, high-speed network connectivity to the rest of the world through a few undersea fiber cables, and traffic imbalance caused by the differential populations of the various countries. Our simulation experiments demonstrate that the concentric two-ring network design is a natural candidate for the African continent.